EP0125153A2 - Method and apparatus for evenly applying a powder coating to a substrate, and substrate thus coated - Google Patents

Abstract

1. Process for uniformly distributing a powder onto a substrate, in which the powder is introduced in suspension into a carrier gas inside a nozzle, and in which a strip of said suspended powder is formed in a gas in proximity to and substantially vertically above (or below) the substrate, characterized in that said strip of suspended powder is formed in a gas as soon as it is introduced into the nozzle, in that said strip is maintained in continuous flow towards the substrate throughout its length, in that gaseous currents are introduced into this strip to create turbulences there and to homogenize the mixture of gas and powder gradually as it progresses towards the substrate, and in that the movement of the powder towards the substrate is regularly accelerated by entraining it by additional gaseous flows introduced at its flanks and directed towards the substrate.

Description

The present invention relates to the homogeneous distribution of a pulverulent product through a slot, on a substrate, in particular glass, with a view to coating it with a film with particular properties, in particular optical or electrical properties.

It is known from patent FR 2 427 141 to distribute continuously on a substrate such as a glass ribbon powdered products suspended in a gas, through a distribution slot arranged above the glass. Said slot is the lower end of a nozzle which comprises a cavity extending over the entire length of the nozzle having in cross section a form of venturi, supplied by a plurality of elementary conduits of the same length resulting from the subdivision of a single powder supply duct suspended in a gas, a broad, approximately parallelepipedal homogenization chamber extending over the entire length of the nozzle into which the venturi-shaped cavity opens and also receiving pressurized gas performing turbulence intended to homogenize the mixture of powder and gas, then following the homogenization chamber and in communication with it by a narrow passage extending over the entire length of the nozzle, a diverging point and then a converging point which terminates to the distribution slot.

This nozzle gives interesting results but it is nevertheless quite sensitive to fouling and periodically requires cleaning to continue to function properly which causes a loss of production. On the other hand it is intended for a length of distribution slot of 250 to 650 mm, and to coat glass ribbons of several meters in width must be placed end to end several identical nozzles. An absolute identity or balancing problem of the different nozzles thus associated then arises to ensure regular distribution over the entire width of the glass. He would be preferred rable to have a single nozzle having a distribution slot of a length equal to several meters in width of the glass ribbon, but it is found that when the nozzle length is significantly increased, the regularity of distribution is disturbed, in particular the trace of the powder feeds by the elementary conduits is found on the glass and the fouling is faster.

The present invention aims to remedy these drawbacks and for this it proposes a method and a device making it possible to cover several meters in width of substrate, in particular the entire width of a glass ribbon manufactured on a "float" installation, in which the fouling is avoided, and thanks to which the regularity of distribution in time and space is obtained.

To obtain the desired regularity of distribution over several meters in width, the method according to the invention is such that it consists in forming a blade of powder suspended in a gas near and substantially perpendicular to the substrate to be coated, in particular above, to standardize the distribution of this powder inside this blade, to homogenize the mixture of gas and powder by admitting additional gas currents, and to regularly accelerate the product blade towards the substrate.

In a first variant, the invention proposes to achieve homogenization and acceleration in two successive stages.

In a second variant, it proposes to achieve homogenization and acceleration in one and the same step.

The invention also provides nozzles for implementing the method.

These nozzles are provided with an opening which passes right through them, at least a portion of this opening which receives the powder to be dispensed at its inlet end at the same time as additional gas streams being regularly convergent.

In a first variant, this regularly convergent zone is preceded by another zone called homogenization zone supplied with powder distributed by separate conduits and receiving at the same level gas streams responsible for creating turbulence to homogenize the distribution of the powder .

In a second variant, this zone is unique, it is directly supplied by means supplying the powder, for example separate conduits, but it is open to the external atmosphere, and the additional gases injected at its inlet and, in a configu special ration where the nozzle is above the substrate, at its upper part, accelerate the powder towards the outlet end, ie downwards when the nozzle is above the substrate, while inducing the entry of external gases which favor homogenization.

Thanks to the invention, the coating technique using powder can be used to obtain coatings with very regular thicknesses, the possible thickness variations being only of the order of 15 to 20 Angstroms, whatever whatever the powder flow rate and / or the thickness of the coating, which leads to variations in light transmission only of the order of 1%.

The coatings obtained can also be very thin, less than 0.1 microns and even of the order of 400 to 800 Angstroms.

Thanks to this technique can even be manufactured industrially, that is to say with a high yield, glazing coated with an interference layer of the 2nd order, blue in color, whose dominant wavelength in reflection is 480 nanometers (nm) and in transmission 575 nm when illuminated by the illuminant standard C.

Interference layers of other colors can a fortiori also be obtained since they allow greater variations in thickness without perceiving the alteration of the color.

• Figure 1 : une buse suivant l'invention comportant une zone d'accélération et une zone d'homogénéisation superposées, montrée en coupe transversale.
• Figure 2 : une variante de buse conforme à l'invention comportant deux zones d'accélération et d'homogénéisation superposées montrée en coupe transversale.
• Figure 3 : une buse suivant l'invention, en coupe transversale, dans laquelle les deux zones d'accélération et d'homogénéisation sont confondues.
• Figure 4 : une vue partielle en coupe longitudinale au niveau des conduits d'alimentation en poudre de la buse de la figure 1.
• Figure 5 : une vue partielle en coupe longitudinale au niveau des conduits d'alimentation de la buse montrée figure 2.

The invention will now be described with reference to the figures which represent:

• Figure 1: a nozzle according to the invention comprising an acceleration zone and a superimposed homogenization zone, shown in cross section.
• Figure 2: a variant of nozzle according to the invention comprising two superposed acceleration and homogenization zones shown in cross section.
• Figure 3: a nozzle according to the invention, in cross section, in which the two acceleration and homogenization zones are combined.
• FIG. 4: a partial view in longitudinal section at the level of the powder supply conduits of the nozzle of FIG. 1.
• FIG. 5: a partial view in longitudinal section at the level of the supply conduits of the nozzle shown in FIG. 2.

Figures 1, 2 and 3 show in cross section of the nozzles 1 and 3 of powder distribution according to the invention. Each extends over the entire width, which can range from about fifty centimeters to several meters, of a substrate 4 to be coated with the powder, the substrate and the nozzle being driven in a translational movement one by compared to each other. This substrate 4 will in particular be a ribbon of glass traveling at uniform speed under the nozzle 1, 2 or 3 kept fixed.

Each nozzle 1, 2 or 3 is formed by a body 5, traversed over its entire height and over its entire length, by a narrow opening 6 in which the powder must circulate and which ends at the outlet end, or low in the configuration shown, by a distribution slot 7. The width of this opening is only about 1 / 50th to 1 / 100th of its height and its variations are relatively small and remain continuous and regular anyway. This opening 6 is supplied, on the one hand with powder to be distributed at its inlet end, in particular upper in the configuration shown, on the other hand with various gas streams.

Side plates 10 close each nozzle 1, 2 or 3 at its ends in the direction of its length.

The nozzle body 5 contains, more particularly in its portion close to the outlet, or low in the configuration shown, cooling members such as 8, for example water circuits, to avoid excessive heating of the nose of nozzle due to the proximity of the support 4 generally brought to a high temperature for powder coating.

The nozzle body 5 also includes various reinforcements or spacers such as 9 ensuring its non-deformability.

Also provided are tie rods, not shown in the figures, acting on the facing walls which delimit the opening 6, these tie rods distributed over the height of the opening allowing precise adjustment of the width of said opening and also reinforcing the non-deformability.

Each nozzle is arranged so that its lower end, or more generally of outlet, is at a distance from the substrate to be coated of approximately 15 to 120 mm, and preferably close to 30 mm.

The nozzles 1 and 2 illustrated in FIGS. 1 and 2 have two zones superimposed in height, an entry zone, still in the configuration shown, upper 11, called homogenization and a lower zone 12 called acceleration, through which the opening 6 extends. In both cases, the opening 6 is ali mented at its inlet or upper part, in powder, generally suspended in a primary gas such as air, by a plurality of supply ducts 13 distributed in the direction of the length of the nozzle, for example regularly distributed about 5 cm from each other and which penetrate through the upper wall 14 of the nozzle body 5, the sealing around these conduits 13 being obtained by means of a cover with holes 15.

In the nozzle 1 (FIG. 1), these conduits 13 extend so as to pass through a gas box, in particular an air box, 16 which, in the configuration shown, overcomes the opening 6 over its entire length, and lead to the opening 6. This gas or air box 16 is supplied with gas or air under pressure by ramps with holes 17 and its bottom 18 being a porous plate of the "Poral" type, this gas or this air is introduced into the opening 6 in a substantially uniform manner over its entire length.

FIG. 4 shows in longitudinal section, that is to say along a median plane arranged along the length of the nozzle, the arrival of the conduits 13 in the opening 6 after crossing the gas or air box 16.

Powder jets suspended in a primary gas, generally air, are introduced quickly, in particular at regular distance intervals into the opening 6 through the conduits 13. Thanks to the gas, in particular to the air which diffuses through the plate 18 of the "Poral" type, turbulences, which standardize the distribution of the powder over the entire length of the nozzle and which homogenize the primary mixture of gas, or air, and powder, supplied by the conduits 13 are created in the zone 11, and the face of the "Poral" plate 18 which forms the ceiling of this zone 11 of the opening 6 is cleaned of any possible fouling.

In the nozzle 2 of FIG. 2, a variant for introducing the homogenization air is presented. The powder supply lines 13 suspended in a gas, in particular air, no longer pass through a gas box, but penetrate directly from the crossing of the upper wall 14 of the nozzle body 5, into a relatively large chamber 40 , extending over the entire length of the nozzle 2 and constituting the upper part of the zone 11 of the opening 6.

The homogenization gas, generally air, is supplied to this chamber 40 by two identical tanks 41, supplied with gas under pressure by ramps with holes 42, arranged on each side of the chamber 40 over its entire length and communicating with it via the side wall 43 that each has in common with it, said wall 43 being of a porous material of the "Poral" type. On leaving the chamber 40, the width of the opening 6 narrows and the supply conduits 13 descend into the chamber 40 until the level of the narrowing is flush. As shown in the longitudinal section of FIG. 5, prism-shaped lamellae 44, arranged transversely, partition jets of powder from each conduit 13 and maintain a substantially constant passage section when the powder released by the conduits 13 enters the opening 6 thus avoiding variations in the speed of the powder and the deposits which could result therefrom on the walls. The homogenization gas in the same way as for the nozzle 1, standardizes the distribution of the powder over the entire length of the nozzle, homogenizes the primary mixture of gas and powder in suspension supplied by the conduits 13, and acts against the powder deposits.

In the two nozzles 1 and 2 shown respectively in FIGS. 1 and 2, the powder after being released by the conduits 13 into the opening 6, undergoing the action of gas and in particular homogenization air, forms a vein of powder suspended in this gas and in particular in the air, in the form of a blade, that is to say a continuous thin vein, having the length of the nozzle, which extends downwards from the nozzle in the configuration shown, between the substantially vertical walls 19 of the zone 11 of the opening 6. Under the effect of the homogenization gas and also under the effect of the increasing distance from screws of the supply conduits, the homogenization of the mixture of gas and powder and the uniformity of its distribution inside the opening 6 are achieved and improve as the powder progresses . Advantageously in the two nozzles 1 and 2, the two walls 19 of the opening 6 which face each other in the homogenization zone 11 converge slightly towards one another. This results in a slight acceleration of the powder and a rolling of the vein in the form of a blade, which further improves the homogeneity and uniformity of the distribution.

In the nozzle 1 of FIG. 1, a slight divergence of the two walls 19 immediately follows the convergence mentioned above. This succession of convergence and divergence on the one hand and the acceleration and then the deceleration of the resulting powder on the other hand, further improve the homogenization and the uniform distribution of the powder.

We can consider that at this level, in the two nozzles 1 and 2, at the end of the homogenization zone 11, the mixture of powder and gas, air in particular, is homogeneous and uniformly distributed over all the surface of the opening 6. Thus, thanks to this zone 11, it has been possible to go from a distribution of powder into separate jets delivered by the conduits 13 to a uniform distribution.

The powder then enters the acceleration zone 12. To obtain sufficient covering of the substrate 4 in a short time, which is particularly necessary in the case of rapid displacement of said substrate, to obtain good adhesion of the powder to the substrate, to prevent the powder from flying off between the time it is released by the distribution slot 7 at the lower end of the nozzle and the moment it comes into contact with the substrate, it is important to give the powder a vertical speed of fall, or more generally of progression towards the substrate 4 , at its exit from the nozzle which is at least of the order of 10 to 15 m / s. On the other hand, since the reaction of the powder on the substrate 4 requires a high temperature, it is also important not to cool the substrate too much and therefore the flow rate of the powder-carrying gas must be limited.

Thus, for example, in the case of spraying powders of organometallic compounds of the DBTO (dibutyl tin oxide) or DBTF (dibutyl tin difluoride) type with a particle size greater than 5 microns and less than 40 microns, onto glass substrates, with a view to the decomposition of these compounds into metal oxides, in particular tin oxide, under the effect of heat, to form a film with specific optical and / or electrical properties, the impact rates of the powder on the glass will be at least equal to 10 m / s and preferences beneficial _- ment between 25 and 45 m / s.

In the two nozzles 1 and 2 presented in FIGS. 1 and 2, the acceleration of the powder in suspension in this gas, the air in particular, and contained in the blade-shaped vein, is obtained in zone 12 of acceleration, by injection of gas and in particular additional air at high speed on the sides of the product blade, over the entire length of the nozzle, and / or by convergence of the portion 20 of the walls 19 facing the zone 12 of the opening 6.

Advantageously, to avoid turbulence liable to create fouling and destroy the homogeneity and uniformity of distribution of the powder mixture in the gas, and in particular in the air, the convergence is regular so as to confer a constant acceleration. Thus the two walls 20 are plane walls making an angle of the order of 7 or 8 ° with the median plane and delimiting at their end a distribution slot of approximately 4 mm in width, that is to say 3 at 4 times narrower than the entrance to the acceleration zone.

In the nozzle 1 shown in fig. 1, the gas and in particular the additional pressurized air is introduced into cavities 21 by ramps 22, each cavity communicating via an orifice 23 having the form of a slot extending over the entire length of the nozzle and of a baffle recess 24, with a lateral chamber 25 adjoining the opening 6 at the start of the acceleration zone 12. Each lateral chamber 25, communicates with the opening 6 by a narrow slot 26, located at the end of the divergent end of the homogenization zone 11, thus introducing on each side of the blade of powder mixture suspended in its carrier gas, gas and in particular air additional, parietal, at high speed, which accelerates mixing.

The pressure drops constituted by the narrow orifices 23, the baffle recess 24, on this additional gas supply make it possible to inject into the opening 6, a uniform gas flow over the entire length.

In the nozzle 2 shown in FIG. 2, cavities 45 supplied with pressurized gas by ramps with holes 46, enclosed in the body 5 of the nozzle are disposed approximately at the midpoint of the nozzle and communicate with the opening 6 through the intermediate of a porous plate 47 of the "Poral" type, then of a slot 48.

The two slots 48 open on each side of the blade of product from the homogenization zone and the gas is injected at the same speed as the blade of powder in suspension. The union of these three streams requires an opening width 46 approximately 3 times greater than at the lower end or more generally at the end of the homogenization zone 11. The meeting of these three currents takes place at the entrance of the acceleration zone 12. The three currents which meet having the same speed, no shearing occurs, the homogeneity and the uniformity obtained at the end of the homogenization zone are preserved.

Then, in the two nozzles 1 and 2, throughout the area acceleration 12, the powder is accelerated due to the convergence of the walls 19, to the end of the nozzle where the powder is released through the distribution slot 7.

Thus all the gas inlets in the opening 6 are strictly controlled in terms of flow and pressure, the nozzles 1 and 2 not being open to the atmosphere, but on the contrary being sealed.

FIG. 3 shows in an alternative embodiment a nozzle 3 in which the homogenization zone and the acceleration zone are combined and in which the inlet of the conduits 13 for supplying powder in suspension in a primary gas, in general l 'air, is no longer performed in a sealed manner.

Indeed, this nozzle is supplied at its inlet, and in the configuration shown at its upper part, by any means capable of introducing powder into the opening 6 over its entire length. As above, it may be supply ducts 13, arranged over the entire length of the nozzle and delivering a plurality of jets, but unlike the previous cases, these ducts only lead to the inlet of the opening. 6 without passage through sealing means. These conduits 13 can be fixed or in motion, for example driven by an alternating movement in the direction of the length of the nozzle, of small amplitude, for example an amplitude of the order of the average spacing between two conduits 13.

The powder falls into the opening 6 which is regularly convergent from the inlet, in particular the top, of the nozzle to the distribution slot 7. The width of the opening 6 at the level of the slot 7 is approximately 3 to 4 times less than its width at the inlet of the nozzle. For example, the width of the opening 6 at the inlet, or at the top, of the nozzle will be approximately 15 mm, at the level of the distribution slot it will be 4 mm, and the flat walls which delimit the opening 6 form an angle of about 5 ° with the median plane.

The two nozzle body halves located on each side of the opening 6 are hollow and each form a series of cavities of gas, and generally of air, under pressure such as 31, each series being connected by a ramp 32 to a source of gas, of air in general, and each cavity being separated from the neighboring cavity of the same series by a partition forming a spacer such as 9 with passages such as 33 is either of porous material of the "Poral" type or by expansion slots, thus making it possible to have at the outlet of the last cavity 31 in the series, a constant flow rate over the entire length of the nozzle.

The compressed gas from each series of cavities 31 is injected into the opening 6, at the inlet, by a calibrated longitudinal blowing slot 34, with lips 35 and 36 formed so as to orient the gas jet injected tangentially to the wall of the opening 6 and more precisely at an angle relative to this wall which remains less than 7 ° so that said jet remains attached to the wall.

The lower lip 35 of each blowing slot 34 is formed by the approximately rounded upper edge of the side wall 37 of the opening 6, while the upper lip 36 is formed by the rounded lower edge of the end part of a plate 38 forming the cover of the cavities such as 31. This edge has a shape complementary to the shape of the lip 35, and extends slightly downward so as to orient the jet of pressurized gas tangentially to the wall.

The calibration of the slot 34 is obtained by sliding the plate 38 in a direction perpendicular to the walls of the opening 6. The gas is injected through the blowing slots 34 at a speed much higher than the speed of the powder to be the outlet of the conduits 13 or any equivalent supply means. Advantageously, this speed is sonic, to increase the acceleration of the mixture and promote the uniform distribution of the flow of gas injected over the entire length of the nozzle.

The end of the conduits 13 is flush with the blowing slots 34. The gas injected through the slots 34 entrains external atmosphere into the opening 6, between the conduits 13. This injected gas and this entrained atmosphere eliminate any risk of unwanted powder deposition on the walls of the opening 6, and also eliminate any risk of powder being discharged through the inlet of the nozzle. Because the opening 6 is in the atmosphere, the modification of the powder supply mode does not imply any intervention on the nozzle itself. In particular, it is possible to modify the spacing of the conduits 13, or to choose another supply means, for example in the case where the nozzle 3 is placed above the substrate 4 to be coated, as shown in FIG. 3, a drum with a horizontal axis provided with pins rotating above the opening 6, loaded with powder which it distributes under the effect of an alternative longitudinal brushing.

In the different variants of nozzles 1, 2 and 3 presented, the outlet end, in particular the bottom of the nozzle body, has an aerodynamic profile of tapered shape so as to favor the training of the ambient atmosphere around the curtain of powder delivered by the distribution slot 7, thus avoiding the formation of turbulence detrimental to the regularity of the flow. This entrainment of ambient air helps to obtain a uniform deposit on the support.

In addition, this end of the nozzle body is provided with heat protection means.

In all the nozzles described we have indicated that the powder is homogenized and / or accelerated by injecting in particular air into the opening 6; of course, one can inject any other gas if desired, for example nitrogen.

In the case of the nozzle 3, it has been indicated that it was an atmospheric nozzle in which the inlet or upper end of the opening 6 was in direct communication with the atmosphere. Of course, if one wishes to work under a controlled atmosphere, or a particular gaseous atmosphere, the upper part of this nozzle will be surmounted by an atmosphere control chamber filled with the desired gas.

In all of the foregoing description, the nozzles 1, 2 and 3 have been described as being arranged vertically above the substrate to be coated and the terms up, down, vertical, horizontal, etc., used relate to this particular configuration taken only as an example.

In fact the nozzles 1, 2 or 3 can take various positions: they can be above or below the substrate to be coated, perfectly vertical or inclined with respect to the vertical, lying horizontally or approximately horizontally if for example the substrate is vertical; the expressions up, down, vertical, horizontal ..., are then to be adapted according to the position of the nozzle.

In all cases, the supply conduits 13 may originate from the division of one or more equivalent elementary conduits, originating from a reserve of powder suspended in a gas, or constituted by an ejector receiving the powder d '' a worm screw located at the base of a hopper filled with powder, diluting it and giving it speed thanks to the addition of pressurized air.

The devices described above make it possible to distribute powders of different natures (organic metallic compounds, plastics, paints, varnishes, enamels, inks, pigments, etc.) on a regular basis on the desired substrates such as glass, metal, wood, paper, etc ...

With a view to the production of glass coated with layers of particular optical qualities, it is possible to distribute various powders based on different metals (tin, indium, titanium, chromium, iron, cobalt, etc.) thus by way of nonlimiting example , powders of dibutyl tin oxide, dibutyl tin difluoride, metallic acetyl acetonates, etc.

The efficiency of these devices is such that they can be used to coat substrates traveling at high speeds up to 10 or 20 m / min. The efficiency is much higher than that which can be obtained with spraying techniques of solutions or C.V.D. (chemical vapor deposition). Of course, these performances can be further improved by combining several nozzles for coating the same substrate.

By using such nozzles, there is also a consumption of active product which can be much lower than that required by other techniques; we thus note weights of powder consumed per m2 of coated substrate, less than 10 g and generally of the order of 3 to 8 grams for layers of the order of 1500 to 2000 Angstrms.

This process and these devices make it possible to obtain layers of reduced thickness, very regular layers whose variations in thickness can be less than 50 Angstroms and even as small as 30 or 40 Angstroms, thus only introducing variations in light transmission on the order of 1% when making "transparent" layers. This good regularity can be obtained on layers of thickness less than a tenth of a micron, and even of the order of 400 to 800 Angstroms. Of course a fortiori the realization of such regular but thicker layers is also possible. This allows the manufacture of anti-static layers. This also allows the deposition of sublayers, for example Ti0 ₂ , favoring the adhesion of subsequent coatings deposited by the same technique and possibly other techniques, techniques under vacuum in particular, these sublayers having to be thin, of the order of 400 to 500 Angstroms, to impair light transmission as little as possible, and perfectly continuous despite the very small thickness.

This also allows the industrial manufacture of interference coating layers, that is to say having a chosen color, without variation of colors due to variations in thicknesses. Thanks to this technique, we can even make coated glasses of a uniform blue layer of order II, of dominant wavelength, in transmission of 575 nanometers and in reflection of 480 nanometers when it is illuminated by the illuminant standard C as defined by the CIE ( International Commission of Lighting). This blue layer being the one for which the thickness differences which do not create interference and also the perceptible chromatic differences are the smallest, a fortiori, the manufacture of layers of another color or neutral shade for which the constraints are less severe, is also possible.

Glazing coated with such layers can be used as automotive glazing (the reductions in light transmission due to said layers are small, so that coated glazing meets the transmission requirement of at least 75% required by regulations) , glazing for housing, in particular heat-resistant glazing, protective walls reflecting heat radiation such as stove portholes, walls of insulating tanks. Substrates other than glass can of course also be coated, for example pipes, metal plates. Glass other than in the form of glazing, for example glass fibers, may be coated.

Examples of conditions for implementing the devices of the invention, and examples of products thus obtained are given below.

EXAMPLE 1

Substrate: float glass, 4 mm thick, running speed 12.50 m / min.

Powder: DBTF with particle size less than 20 microns, flow rate: 5.6 kg per hour and per linear meter of nozzle length.

Nozzle: nozzle used identical to the nozzle shown in fig. 3, width of the distribution slot referenced 7: 4.5 mm, distance between the lower end of the nozzle and the glass: 90 mm primary gas in which the powder is in suspension on arrival via the conduits 13: nitrogen at the right level of 135 Nm3 per hour and per linear meter of nozzle length, gas injected through the slots 37: nitrogen at the rate of 335 Nm3 per hour and per linear meter of nozzle length, Atmospheric air aspirated: 125 Nm3 per hour and per linear meter nozzle length. Layer obtained: Fluorescent doped Sn0 ₂ monolayer, between 1635 and 1650 Angstroms, with thickness differences of 15 Angstroms, emissivity coefficient of the layer at 393 ° K: 0.3, light transmission : 83% ± 1%, color: bluish in reflection,

slightly amber in transmission.

EXAMPLE 2

Substrate: glass 6 mm thick, running speed 6 m / min.

Powder: mixture of 25% Fe acetyl acetonate, 25% Cr acetyl acetonate, 50% CoII acetyl acetonate, flow rate: 1,200 kg per hour and per linear meter of nozzle. Nozzle: identical to that shown in fig. 1. glass-nozzle distance: 90 mm, primary gas: air at 200 Nm ³ per hour and per meter of nozzle length, homogenization gas: air at 60 Nm3 per hour and per meter of nozzle, acceleration gas: air at 250 Nm ³ per hour and per meter of nozzle. Layer obtained: light transmission 44% ± 1% light reflection 34% ± 1%.

EXAMPLE 3

Substrate: 4 mm thick float glass. Powder: DBTF. Nozzle: identical to that shown in fig. 3. Layer obtained: single layer of Sn0 ₂ doped with fluorine, thickness: 2400 to 2450 Angstroms, color: golden yellow in reflection, slightly bluish in transmission. emissivity coefficient: 0.25 to 393 ° K, light transmission: 76% ± 1%.

Claims (47)

1. A method for regularly distributing a powder on a substrate, characterized in that it consists essentially in forming near and substantially above the substrate a vein of powder suspended in a gas in the form of a blade over a length at least equal to the width of the substrate to be coated, to maintain said vein in continuous flow towards the substrate over its entire length, to introduce gas streams into this vein to create turbulence and homogenize the mixture of gas and powder in the as it progresses towards the substrate, to regularly accelerate the movement of the powder towards the substrate by entraining it by additional gas streams introduced on its sides towards the substrate. 2. Method according to claim 1, characterized in that immediately before the contact of the powder with the substrate is favored the entrainment by induction of the ambient atmosphere, by the current of powder in suspension in the gas, released at high speed . 3. Method according to one of claims 1 or 2, characterized in that the thickness of the blade of powder in suspension becomes narrower as one approaches the substrate so as to accelerate the powder. 4. Method according to one of the preceding claims, characterized in that the speed of the powder in the entire area where it is accelerated is greater than 10 m / s. 5. Method according to one of the preceding claims, characterized in that the blade is given a width of the order of 1 / 50th to 1 / 1OD ^e of its height. 6. Method according to one of the preceding claims, characterized in that the additional gas streams are uniform lamellar streams over the entire length of the blade, introduced on either side of said blade, so as to envelop it. 7. Method according to one of the preceding claims, characterized in that the additional currents are parietal. 8. Method according to any one of the preceding claims, characterized in that in a first step, turbulence is created to homogenize the mixture of gas and powder and in that in a second step separate from the first one accelerates the movement of the powder. 9. Method according to claim 8, characterized in that additional currents to accelerate the powder are introduced at the same speed as the powder in suspension at the meeting point. 10. Method according to claim 8, characterized in that the additional currents are introduced at a speed greater than that of the powder at the time of the encounter. 11. Method according to one of claims 8 to 10, characterized in that the mixture of gas and powder is homogenized in the blade by modulating the width of said blade before accelerating convergence or convergence followed by divergence. 12. Method according to one of claims 8 to 11, characterized in that all the gases entering the blade are injected under pressure and controlled flow. 13. Method according to one of claims 1 to 7, characterized in that the mixture of powder and gas is accelerated and homogenized in a single step, the additional gas streams being introduced at a speed greater than that of the powder when it meets said currents. 14. Method according to claim 13, characterized in that the additional currents introduced at high speed carry out an aspiration of the surrounding atmosphere. 15. Application of the method according to one of the preceding claims to the deposition of a powder having a particle size of the order of 20 microns, and preferably between 5 and 40 microns, of organo-metallic compounds of the DBTO or DBTF or acetyl type. metallic acetonates for pyrolysis on a glass ribbon brought to high temperature. 16. Application according to claim 15, characterized in that the outlet end of the nozzle is disposed at a distance from the substrate to be coated between 15 and 120 mm and preferably close to 30 mm. 17. Application according to one of claims 15 or 16, characterized in that the powder at the outlet of the nozzle is sprayed towards the substrate with a speed greater than 10 m / s and preferably between 25 and 45 m / s. 18. Nozzle for spraying powder onto a support, characterized in that it has an opening passing right through it, terminated by a longitudinal distribution slot, said opening having at least one zone called the acceleration zone immediately preceding the distribution slot, constantly converging formed by two walls facing each other, spaced apart delimiting a blade-shaped space, receiving powder at its entrance, also receiving at this entrance, on its sides, along its side walls, a gas called d acceleration, directed towards the other end of the nozzle. 19. Nozzle according to claim 18, characterized in that the convergence of the acceleration zone is such that the width of said zone at the level of the distribution slot is approximately 3 to 4 times narrower than at the level where it receives the powder and where it is supplied with accelerating gas. 20. Nozzle according to claim 19, characterized in that the dispensing slot is at most 5 mm in width. 21. Nozzle according to one of claims 18 to 20, characterized in that the acceleration gas supply slots are directed towards the substrate. 22. Nozzle according to one of claims 18 to 21, characterized in that the opening passing through it also comprises a homogenization zone which precedes the acceleration zone and which supplies it with powder, the homogenization zone being it even supplied with powder by a plurality of supply conduits distributed in the longitudinal direction of the nozzle, opening in leaktight manner at the start of said zone, means for blowing a homogenization gas intended to create turbulence also opening at same level. 23. Nozzle according to claim 22, characterized in that the means for blowing the homogenization gas comprise cavities supplied with gas under pressure communicating with the homogenization zone by means of porous plates. 24. Nozzle according to claim 23, characterized in that the homogenization zone is a narrow zone making the entire length of the nozzle, limited by two walls which face each other, substantially parallel, thus delimiting a space in the form of a blade. 25. Nozzle according to one of claims 22 to 24, characterized in that the walls limiting the acceleration zone form an angle of the order of 7 or 8 ° with the median plane. 26. Nozzle according to one of claims 22 to 25, characterized in that the inlets of the powder supply conduits are partitioned by the lamellae arranged transversely and having the shape of prisms whose tip is turned towards the substrate, so to conserve the section at the passage of the powder supply conduits at the opening passing through the nozzle. 27. Nozzle according to one of claims 22 to 26, characterized in that the sections of the acceleration gas supply slots are such that the acceleration gas and the powder in suspension meet while being at the same speed . 28. Nozzle according to one of claims 22 to 26, characterized in that the acceleration gas is supplied by slots shaped so that the currents of this acceleration gas are parietal, these slots being supplied so that the currents have a high speed greater than that of the powder. 29. Nozzle according to one of claims 18 to 21, characterized in that powder supply conduits distributed in the longitudinal direction open directly at the start of the acceleration zone. 30. Nozzle according to claim 29, characterized in that the conduits are driven in an alternating movement in the direction of its length. 31. Nozzle according to one of claims 18 to 21, characterized in that it is supplied with powder directly at the start of the acceleration zone by a distributor comprising a spiked drum rotating around a horizontal axis, loaded with powder, extracted by a brush with alternating horizontal movement. 32. Nozzle according to one of claims 29 to 31, characterized in that the acceleration gas is introduced through calibrated slots shaped so that the angle of introduction of the gas makes an angle with the wall of the acceleration zone, which does not exceed 7 °. 33. Nozzle according to one of claims 18 to 21, 29 to 32, characterized in that the acceleration gas is supplied by a plurality of cavities in series, the first being supplied with gas under pressure and communicating with the following by porous plates or expansion slots, the last of the cavities in the series supplying gas to the acceleration zone through a narrow calibrated slot. 34. Nozzle according to claim 33, characterized in that the gas is supplied at sonic speed. 35. Nozzle according to one of claims 29 to 34, characterized in that the entrance to the acceleration zone is in the free atmosphere. 36. Nozzle according to one of claims 29 to 34, characterized in that the entrance to the acceleration zone is surmounted by an atmosphere control chamber supplied with a controlled atmosphere. 37. Nozzle according to one of claims 29 to 36, characterized in that the walls of the opening form an angle of the order of 5 ° with median plane. 38. Nozzle according to one of claims 18 to 37, characterized in that the nozzle nose is tapered. 39. Nozzle according to one of claims 18 to 38, characterized in that the nozzle nose has thermal protection and cooling means. 40. Nozzle according to one of claims 18 to 39, characterized in that the width of the opening is of the order of 1/50 ^th to 1 / i00th of its height. 41. Product formed of a substrate covered with a coating obtained by depositing a powder according to the method of one of claims 1 to 14, characterized in that the coating has thickness variations capable of being less at 50 Angstroms and even on the order of 30 to 40 Angstroms. 42. Product according to claim 41, characterized in that the substrate being a sheet of glass, the regularity of the coating is such that the variations in light transmission are of the order of one percent. 43. Product according to one of claims 41 or 42, characterized in that the coating is a layer of Sn0 ₂ doped with fluorine, whose dominant wavelength under illumination by the source C is in reflection 480 nm and in transmission 575 nm, uniform in color. 44. Product according to one of claims 41 or 42, characterized in that it has a coating of thickness less than 0.1 micron, and even of the order of 400 to 800 Angstroms. 45. Product according to claim 44, characterized in that the coating is a continuous layer of Ti0 ₂ with a thickness of the order of 500 Angstroms. 46. Product according to one of claims 41 or 42, characterized in that the substrate being a glass sheet, in particular 4 mm thick, the deposited layer being tin oxide doped with fluorine, the emissivity is at most around 0.3 and the light transmission is greater than 75%, making it possible to use it as a windshield for cars and in general as glazing for cars. 47. Application of the product according to one of claims 41 to 46, for use as an anti-heat or heat-reflecting wall, in particular for portholes for cookers or the like, or for insulating tanks.

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